Various types of NOx sensors have been proposed for use in engine control to improve performance and reduce emissions. In one example, an electronically heated dual pumping cell (chamber) type sensor is used that provides both oxygen concentration and NOx concentration.
In general, a first voltage is applied across the first pumping cell which results in oxygen being pumped out of a first chamber. The first chamber may be connected to the ambient measurement gas through an aperture or porous diffusion barrier. Once all of the oxygen has been removed from the chamber, the pumping current saturates at a level proportional to the rate of oxygen diffusing into the first chamber. The limiting current from the first cell can be a measure of the oxygen concentration in the measurement gas and can be proportional to air/fuel ratio. The pumping current from this first cell may be on the order of milliamps in engine exhaust applications.
The second pumping cell in the sensor dissociates the NOx and pumps out the oxygen liberated from the dissociation. The pumping current output from the second cell can be a measure of the NOx concentration. This second pump cell may be located in a second chamber adjacent to the first chamber and connected by another aperture or porous diffusion barrier. However, because in engine exhaust application NOx concentrations may be significantly lower than oxygen concentrations, and because NOx must diffuse through 2 separate diffusion barriers, the oxygen pumped by the second cell from the dissociation of NOx may be very small. Therefore, the resulting limiting pumping current may also be very small (on the order of nanoamps), as compared to the milliamps arising from the first cell.
In prior approaches, such as U.S. Pat. No. 6,309,536, separate electronic processing (including A/D converters) from the engine control unit has been used to provide accurate sensing of both oxygen and NOx. It is presumed that such redundant processing is needed in close proximity to the sensor to process the pump currents and control the heater. In other words, long signal wires between the sensor and electronics may result in loss of signal and increased noise. Thus, the small pumping current may limit the distance between the signal processing electronics and the sensor (thereby resulting in multiple processing units), and may also require fairly sophisticated ammeters to accurately measure the signal.
The inventors herein have recognized a disadvantage with such an approach. In particular, providing separate processing electronics, especially in close proximity to the sensor, may create numerous issues. First, cost is significantly increased due to the electronics, and cost is further increased due to the harsh exhaust environment that these electronics must endure.
The above issues may be addressed by, a system for a vehicle having an internal combustion engine, the system comprising:
a sensor adapted to be coupled into an exhaust of the engine, said sensor outputting at least a first signal indicative of oxygen and a second signal indicative of NOx;
a controller receiving at least said first and second signal, said controller processing said first and second signal, and controlling said engine by adjusting an engine actuator based on at least one of said first and second processed signals; and
a transmission amplifier coupled to said sensor configured to amplify said second signal before it is transmitted to and received by said controller.
In another embodiment, the above issues may be addressed by a system for a vehicle having an internal combustion engine, the system comprising:
a sensor adapted to be coupled into an exhaust of the engine, where exhaust gas enters at least a first pumping cell that outputs at least a first signal indicative of oxygen, and then enters a second pumping cell through an passage, the second cell outputs at least a second signal indicative of NOx, and the passage configured to produce said second signal such that it can be transmitted to a controller;
said controller receiving at least said first and second signal, said controller processing said first and second signal, and controlling said engine by adjusting an engine actuator based on at least one of said first and second processed signals.
As such, the inventors herein have recognized that the NOx signal current levels are driving the use of a processor and other electronics close to the sensor. Further, they have also recognized that only the NOx signal generally is of low pumping current levels. Thus, in one example, the current forming the NOx signal is amplified such that wiring losses are reduced and the processing electronics, including the NOx and oxygen signal and heater control electronics can be moved to the engine control unit. In another example, a NOx sensor structure is provided to increase current forming the NOx signal such that wiring losses are reduced and the processing electronics, including the NOx and oxygen signal and heater control electronics can be moved to the engine control unit. These embodiments may also be used in combination, if desired.
Note that there are various types of transmission amplifiers, and various types of NOx sensors that provide at least a first and second output. Further, while the above example relates to NOx sensing, the approach can be applied to any oxygen containing species, such as SOx, CO2, and/or H2O, for example.